Diffraction data were collected from a cryoprotected (30% glucose) apolipoprotein A-I apo ((1 43)A-I crystal (P212121, a = 97.47, b = 113.87, c = 196.19 ) at CHESS beamline A-1 on 13 July 1997 (100 K, 70 0.5' oscillation frames, 60 sec, 130 mm detector distance). The data were integrated with MOSFLM, scaled with SCALA, and further processed with the CCP4 suite. These data are 57% complete to 3.0 resolution, with an Rsym of 11.4% (37.9% in the 3.2 3.0 shell). These data are dramatically better than those that we collected in our laboratory and used to solve the structure at 4 resolution. Even at 100 K, however, these crystals remain extremely sensitive to radiation damage, diffracting to 3 for only 30 min. Our use of CHESS beamline A-1 on this project has validated the notion that these apo ((1 43)A-I crystals diffract to better that 4 resolution. Additional data collection at CHESS is planned to complete these data, so that refinement at 3 can commence. We also look forward to future data collection at CHESS from our low-salt I222 apo ((1 43)A-I crystal form, and crystals of other forms of apo A-I under study in our laboratories.